Intranight Optical Variability of Radio-Quiet Weak Emission Line Quasars-IV

TL;DR

This study investigates the intra-night optical variability of radio-quiet weak emission line quasars to understand their potential as BL Lac candidates, finding low overall variability but some blazar-like events.

Contribution

It extends previous research by monitoring a well-defined sample of RQWLQs, providing new data on their variability and assessing their similarity to blazars.

Findings

INOV duty cycle of ~3% for RQWLQs

Strong variability events observed in 2 sessions

Potential for higher INOV detection with improved sensitivity

Abstract

We report an extension of our program to search for radio-quiet BL Lac candidates using intra-night optical variability (INOV) as a probe. The present INOV observations cover a well-defined representative set of 10 `radio-quiet weak-emission-line quasars' (RQWLQs), selected from a newly published sample of 46 such sources, derived from the Sloan Digital Sky Survey (Data release 7). Intra-night CCD monitoring of the 10 RQWLQs was carried out in 18 sessions lasting at least 3.5 hours. For each session, differential light curves (DLCs) of the target RQWLQ were derived relative to two steady comparison stars monitored simultaneously. Combining these new data with those already published by us for 15 RQWLQs monitored in 30 sessions, we estimate an INOV duty cycle of $\sim 3\%$ for the RQWLQs, which appears inconsistent with BL Lacs. However, the observed INOV events (which occurred in just two of the sessions) are strong (with a fractional variability amplitude $\psi >$ 10\%), hence blazar-like. We briefly point out the prospects of an appreciable rise in the estimated INOV duty cycle for RQWLQs with a relatively modest increase in sensitivity for monitoring these rather faint objects.